Minimally invasive spinal stabilization system

ABSTRACT

A spinal stabilization system includes an implant and instrumentation for stabilizing the spine. In one embodiment, the system includes a plate having a side rail and a channel extending adjacent the side rail. A pedicle screw assembly is positioned in the channel in releasable engagement with the side rail. The pedicle screw assembly includes a polyaxial screw seated in a lower housing having a lower locking flange. An upper housing having an upper locking flange secures the plate to the lower housing. The side rail of the plate is releasably engaged between the upper locking flange and the lower locking flange. The upper and lower housings include on-board locking mechanisms for fixing components in the screw assembly. The screw assembly and plate are inserted and oriented by remote manipulation. Minimally invasive techniques for inserting the implant are performed with the instrumentation, and cause minimal disturbance to surrounding tissue.

FIELD OF THE INVENTION

The present invention relates generally to surgical implants forstabilizing the spine, and more particularly to a spinal implant system,instrumentation and surgical procedures for inserting and manipulating aspinal implant system in a minimally invasive manner.

BACKGROUND OF THE INVENTION

Spinal surgery on the lumbar and thoracic spines have classically beenopen operations, meaning that the instrumentation used is placed throughan incision that exposes all of the spine to be instrumented, as well asa portion of spine above and below the area to be instrumented due tothe need for proper visualization. This extensive exposure disrupts aconsiderable amount of tissue, particularly the lumbar paraspinalmusculature which needs to be stripped off the vertebra bones forexposure. This stripping leads to muscle damage directly caused byeither electrical cautery or manual cutting or indirectly byinterruption of vascular supply to the muscle due to coagulation orcutting of vessels, and caused also by embarrassment of the vascularsupply during the course of surgery due to compression by retractors onthe muscle which are required to maintain exposure. In addition, spinalimplants can impact upon the facet joints of the spine, particularly theupper most pair of pedicle screws, which can cause pain or dysfunctionof the involved joint. This is due in part to the fact that the pediclescrew systems are designed to give stability without being made torespect normal anatomy. In other words, the spine is forced to fit themetal, instead of fitting the metal to the spine.

The present day surgical approach therefore has added to patientmorbidity due to the extent of the surgical exposure, tissue damage doneprimarily to the posterior longitudinal musculature of the spine duringthe exposure, blood loss and risk of infection. Large open operationsalso tend to be the cause of significant postoperative pain anddisability. Accordingly, these issues lead to longer hospital stays,higher postoperative complications, such as phlebitis and pneumoniabrought on by immobility, and greater consumption of postoperativemedications with their resultant side effects. In addition, theparaspinal muscle tissue damage has been implicated in the genesis ofpostoperative lumbar mechanical dysfunction and stiffness leading topostoperative pain syndromes or failed back syndrome. Also, interferenceby metal implants of the normal function of the rostral facet joints hasbeen implicated in the early degeneration of these joints, as well aspain and disability, all which could lead to other more involvedsurgeries.

SUMMARY OF THE INVENTION

The foregoing limitations of conventional spinal stabilizationinstrumentation, implants and procedures are resolved in severalrespects by minimally invasive systems and methods in accordance withthe invention. In a first embodiment of the invention, a spinalstabilization system includes an elongated plate having a side rail anda channel extending adjacent the side rail. A pedicle screw assembly ispositioned in the channel in releasable engagement with the side rail.The pedicle screw assembly includes a polyaxial screw having a roundedhead and an elongated shank, and a lower screw housing having a lowerlocking flange and a seat portion. The polyaxial screw extends throughthe lower screw housing with the rounded head engaging the seat portion.The pedicle screw assembly also includes a lower locking elementpositioned in the lower screw housing to secure the polyaxial screw headin the lower screw housing, and an upper screw housing having a boreproviding access to the lower locking element and the polyaxial screw,the upper screw housing having an upper locking flange. The side rail ofthe plate is releasably engaged between the upper locking flange and thelower locking flange. An upper locking element couples the upper screwhousing to the lower screw housing and secures the rail between theupper locking flange and the lower locking flange.

In a second embodiment of the invention, a pedicle screw assemblyincludes a polyaxial screw having a rounded head and an elongated shank,and a lower screw housing having a lower locking flange extendingradially outwardly. The polyaxial screw extends through the lower screwhousing with the rounded head engaging the seat portion. A lower lockingelement positioned in the lower screw housing secures the polyaxialscrew head in the lower screw housing. An upper screw housing includes abore providing access to the lower locking element and the polyaxialscrew, and an upper locking flange extending radially outwardly. Anupper locking element couples the upper screw housing to the lower screwhousing.

In a third embodiment of the invention, a spinal stabilization plateincludes an elongated body having a pair of generally parallel siderails and a channel extending between the side rails. The body furtherincludes a first end having an aperture that connects with the channelby way of a passage through the first end, and a second end opposite thefirst end. The side rails each include an upper surface with a pluralityof clamping recesses and an inner sidewall facing along the channel witha groove extending parallel with the channel.

In a fourth embodiment of the invention, a guidewire insertion kitincludes a casing having a proximal end and a distal end, and forming abore extending from the proximal end to the distal end. The kit alsoincludes a hammer having a bore in which the proximal end of the casingextends, the hammer being slidably displaceable along the casing. Aguidewire extends through the bore of the casing.

In a fifth embodiment of the invention, an assembly for orienting aspinal stabilization plate includes an obturator having a probe end withat least one retractable locking tab. The locking tab is displaceablebetween a locking position, in which the locking tab extends radiallyoutwardly from the probe end, and a release position, in which thelocking tab is retracted inside the probe end. A plate reduction sleeveincludes a tubular wall and a bore extending along the length of thetubular wall. The obturator extends within the bore of the platereduction sleeve and slidably engages the tubular wall. The tubular wallincludes at least one alignment member that engages the obturator tosubstantially prevent rotation of the obturator in the plate reductionsleeve.

In a sixth embodiment of the invention, an assembly for introducing abone screw assembly to a spinal stabilization plate includes a sleevehaving a tubular wall and a passage extending along the length of thetubular wall. The tubular wall includes a proximal end having an openinginto the passage, and a distal end having a clamping member fordetachably engaging a stabilization plate. A screw housing manipulatorincludes a tubular wall and a bore extending along the length of thetubular wall, the tubular wall having a proximal end having an openinginto the bore, and a distal end having a clamping member for detachablyengaging a screw assembly. The screw housing manipulator is slidablydisplaceable and rotatable in the passage of the sleeve. In oneembodiment, the screw housing manipulator is rotatable in the passage ofthe sleeve within a limited range of approximately ninety degrees in onedirection.

In a seventh embodiment of the invention, a method for implanting aminimally invasive spinal stabilization plate includes the steps ofinserting an elongated plate into a space above a first vertebra and asecond vertebra that is being fused to the first vertebra; driving afirst screw assembly through a channel extending within the plate andinto the first vertebra, the first screw assembly having an on-boardlocking mechanism; locking the first screw assembly to the plate;driving a second screw assembly through the channel within the plate andinto the second vertebra, the second screw assembly having an on-boardlocking mechanism; locking the second screw assembly to the plate;moving the second screw assembly toward the first screw assembly toapply compression between the first and second vertebrae; and lockingdown the first screw assembly and the second screw assembly to fix theorientation of the plate.

In an eighth embodiment of the invention, a method for implanting aminimally invasive spinal stabilization plate includes the steps ofdriving a guidewire into a vertebra; inserting a plate over thevertebra, the plate having a pair of side rails and a channel betweenthe side rails; advancing a first instrument over the guidewire tocenter the guidewire between the side rails; advancing a secondinstrument over the guidewire to draw the plate perpendicular to theguidewire; advancing a screw assembly over the guidewire and into thechannel, the screw assembly having a housing and a screw thatarticulates with respect to the housing; driving the screw into thevertebra to fix the screw relative to the vertebra; locking the housingof the screw assembly to the plate; and locking the screw to the housingto fix the housing and plate relative to the vertebra.

In a ninth embodiment of the invention, an instrument for inserting andremotely operating a spinal stabilization system includes an outer shafthaving a distal end and a coupling on the distal end for engaging aspinal stabilization plate. An inner shaft is axially displaceableinside the outer shaft. A first driving mechanism engages the outershaft and operates to attach the outer shaft to a spinal stabilizationplate. A second driving mechanism engages the inner shaft and operatesto axially advance the inner shaft through the outer shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary and the following description will be more clearlyunderstood in conjunction with the drawing figures, of which:

FIG. 1 is a perspective view of a spinal stabilization system inaccordance with one exemplary embodiment of the invention;

FIG. 2 is a perspective view of a polyaxial screw assembly in accordancewith one exemplary embodiment of the invention;

FIG. 3 is a cross-sectional view of the polyaxial screw assembly of FIG.2;

FIG. 4A is a perspective view of a housing component in the polyaxialscrew assembly of FIG. 2;

FIG. 4B is an elevation view of the housing component of FIG. 4A, shownin partial cross section;

FIG. 5 is a top view of the housing component of FIG. 4A;

FIG. 6A is a perspective view of another housing component in thepolyaxial screw assembly of FIG. 2;

FIG. 6B is a top view of the housing component of FIG. 6A;

FIG. 7 is a perspective view of a plate in accordance with one exemplaryembodiment of the invention;

FIG. 8 is a top view of the plate of FIG. 7;

FIG. 9 is a truncated top cross-sectional view of the plate of FIG. 7;

FIG. 10 is a side cross-sectional view of the plate of FIG. 7;

FIG. 11 is a cross-sectional view of the plate of FIG. 7 taken throughline 11-11 in FIG. 10;

FIG. 11A is an elevation view of a housing component in accordance withan alternate embodiment of the invention, shown in partialcross-section;

FIG. 11B is a cross-sectional view of a plate in accordance with analternate embodiment of the invention, shown in cross-section;

FIG. 12 is an elevation view of a guidewire insertion assembly inaccordance with one exemplary embodiment of the invention;

FIG. 13 is a perspective view of an inserted handle of the guidewireinsertion assembly of FIG. 12;

FIG. 14 is an elevation view of a dilator component in accordance withone exemplary embodiment of the invention;

FIG. 15 is a perspective view of another dilator component in accordancewith one exemplary embodiment of the invention, which may be integrallyformed with or attached to other components;

FIG. 16 is an exploded elevation view of a plate orientation assembly inaccordance with one exemplary embodiment of the invention;

FIG. 17 is a first side view of an obturator assembly in accordance withone exemplary embodiment of the invention;

FIG. 18 is a second side view of the obturator assembly of FIG. 17;

FIG. 19 is a cross-sectional view of the obturator assembly of FIG. 17,taken through line 19-19 in FIG. 17;

FIG. 20 is an end view of one component of the obturator assembly shownin FIG. 17;

FIG. 21 is an enlarged side view of an inner shaft of the obturatorassembly of FIG. 17, shown in partial cross section;

FIG. 22 is a cross-sectional end view of the inner shaft of FIG. 21taken through line 22-22 of FIG. 21;

FIG. 23 is a first side view of a plate reduction sleeve assembly inaccordance with one exemplary embodiment of the invention;

FIG. 23A is a proximal end view of the plate reduction sleeve assemblyof FIG. 23;

FIG. 24 is a second side view of the plate reduction sleeve assembly ofFIG. 23;

FIG. 25 is a side view of an outer shaft of the plate reduction sleeveassembly of FIG. 23;

FIG. 26 is a side cross-sectional view of the outer shaft of FIG. 25,taken through line 26-26 in FIG. 25;

FIG. 27 is a first side view of an inner shaft of the plate reductionsleeve assembly of FIG. 23;

FIG. 28 is a second side view of an inner shaft of the plate reductionsleeve assembly of FIG. 23;

FIG. 29 is a knob component of the plate reduction sleeve assembly ofFIG. 23;

FIG. 30 is a perspective view of a screw housing manipulator assembly inaccordance with one exemplary embodiment of the invention;

FIG. 31 is a cross-sectional view of the screw housing manipulatorassembly of FIG. 30;

FIG. 32 is a first side view of an inner shaft of the screw housingmanipulator assembly of FIG. 30;

FIG. 33 is a second side view of an inner shaft of the screw housingmanipulator assembly of FIG. 30;

FIG. 34 is an enlarged cross-sectional view of an end of the inner shaftof the screw housing manipulator assembly of FIG. 30;

FIG. 35 is a side view of an outer shaft of the screw housingmanipulator assembly of FIG. 30;

FIG. 36 is a side cross-sectional view of the outer shaft of the screwhousing manipulator assembly of FIG. 30, taken though line 36-36 of FIG.35;

FIG. 37 is a side cross-sectional view of a collar component of thescrew housing manipulator assembly of FIG. 30;

FIG. 38 is a perspective view of a sleeve component of a counter-torquekit in accordance with one exemplary embodiment of the invention;

FIG. 39A is a side view of the sleeve of FIG. 38;

FIG. 39B is a side cross-sectional view of the sleeve of FIG. 38, takenthrough line 39B-39B of FIG. 39A;

FIG. 40 is a side view of a counter-torque handle used in acounter-torque kit in accordance with one exemplary embodiment of theinvention;

FIG. 41 is a cross-sectional view of the counter-torque handle of FIG.40, taken through line 41-41 of FIG. 40;

FIG. 42 is a perspective view of an inserter according to an exemplaryembodiment of the present invention shown with a stabilization plate;

FIG. 43 is a top plan view of the inserter shown in FIG. 42;

FIG. 44 is a cross-sectional view of a portion of the inserter takenthrough lines 44-44 of FIG. 43;

FIG. 45 is a top plan view of a handle body of the inserter shown inFIG. 42;

FIG. 46 is a perspective view of a handle portion of the inserter shownin FIG. 42;

FIG. 47 is a side elevation view of a rack of the inserter shown in FIG.42;

FIG. 48 is a side elevation view of a ratchet lever of the insertershown in FIG. 42;

FIG. 49 is a cross-sectional view of an inserter knob of the insertertaken along lines 49-49 of FIG. 44;

FIG. 50 is a perspective view of a sleeve that engages with the inserterknob of FIG. 49 and is mated with a flexible outer shaft;

FIG. 51 is an end view of the sleeve of FIG. 50;

FIG. 52 is a side cross-sectional view of the sleeve of FIG. 50;

FIG. 53 is a side elevation view of an inserter shaft of the insertershown in FIG. 42;

FIG. 54 is a cross-sectional view of a portion of the inserter shafttaken along line 54-54 of FIG. 53;

FIG. 55 is an end view of a retaining ring used in the inserter shaftshown in FIG. 53;

FIG. 56 is a perspective view of an inserter tip used in the insertershaft shown in FIG. 53;

FIG. 57 is a side elevation view of the inserter tip shown in FIG. 56;

FIG. 58 is a side elevation view of a flexible outer shaft of theinserter shown in FIG. 42;

FIG. 59 is an enlarged view of the distal tip of the outer shaft shownin FIG. 58;

FIG. 60 is a cross-sectional view of the distal tip taken along line60-60 of FIG. 59;

FIG. 61 is a side elevation view of a flexible inner shaft of theinserter shown in FIG. 42;

FIG. 62 is a side elevation view of the inner shaft of FIG. 61, withproximal and distal ends of the shaft removed;

FIG. 63 is an enlarged view of the distal tip of the inner shaft shownin FIG. 61;

FIG. 64 is a cross-sectional view of the distal tip of the inner shaftshown in FIG. 61 taken along line 64-64 of FIG. 63; and

FIG. 65 is a block diagram outlining a procedure in accordance with oneexemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

The apparatuses and methodology that are used in accordance with theinvention provide a muscle sparing technique for stabilizing the spinethat minimizes the disruption and damage of tissue. Rather thanstripping a large section of tissue from bone to expose the spine, theapparatuses and methods described in accordance with the invention passpercutaneously through a small incision and displace only a small areaof tissue. Once the stabilization assembly is properly positioned, theassembly is adjusted through the small incision, requiring minimaldisruption of surrounding tissue. The instrumentation provides audibleand tactical signals during operation so that the need for directvisualization of the implant is reduced or eliminated. When the need forvisualization of the implant below tissue is required, the implant andinstrumentation are detectable through lateral imaging techniques,avoiding the need once again to open a large area of tissue. Inpreferred embodiments, selected portions of the instruments areradiolucent to allow the surgeon to properly visualize and monitor eachsurgical step. The apparatuses and methodology of the present inventionprovide minimally invasive techniques in all stages of operation,including spinal access, implant insertion, implant manipulation, spinalcompression and final tightening of the implant.

Referring now to the drawing figures generally, various assemblies andcomponents in accordance with the invention will be described. FIG. 1illustrates a minimally invasive spinal stabilization system 10 inaccordance with one possible embodiment of the invention. Stabilizationsystem 10 can be implanted over two or more vertebral bodies tostabilize them against relative motion. Various implant sizes andconfigurations are possible, as dictated by the patient's condition, andother factors. System 10, for example, includes two polyaxial pediclescrew assemblies 100 that cooperate with a bone plate 200. Each screwassembly 100 can be inserted through a channel 250 in plate 200 andanchored into a vertebral body. The position of each screw assembly 100can further be adjusted with respect to the plate, and then tightened tosecure the plate to the spine. Each screw assembly 100 contains on-boardlocking mechanisms to fix the polyaxial screw head in the assembly oncethe assembly is locked to the plate 200. As will be described, the stepsof accessing the spine and positioning and tightening stabilizationsystem 10 require minimal disturbance of tissue and blood vessels aroundthe spine.

Referring now to FIGS. 2 and 3, screw assembly 100 includes a polyaxialscrew 110 having a head 112 and a shank 120. Screw 110 is cannulated toallow it to be introduced over a surgically placed guidewire. Head 112and shank 120 are both cannulated, forming a bore 124 that extends theentire length of screw 110. A number of screw configurations may be usedin accordance with the invention, including one-piece screws or modularscrew assemblies. In screw 110, head 112 is threaded into shank 120,with the head and shank essentially operating as a single integral body.Head 112 includes a rounded portion 114 to allow for polyaxial mobilityand engagement with the rest of screw assembly 100. Rounded portion 114may include contours that are spherical, parabolic, or of a compoundcurvature. The assemblies of the present invention preferably utilizescrews with surfaces that form a strong locking engagement with the restof the screw assembly in the tightened condition. Rounded portion 114,for example, includes a jagged surface 116 that bites into adjacentsurfaces in screw assembly 100 when polyaxial screw 110 is tightened inthe assembly.

A number of components within screw assembly 100 have sockets forengagement with insertion tools and driving tools. A variety of standardor customized socket configurations may be used in accordance with theinvention. For purposes of this description, hexagonal configurationswill be shown and described, with the understanding that otherconfigurations may be used. Screw 110 includes a hexagonal socket 118 inscrew head 112. Hexagonal socket 118 cooperates with a hex driver, totighten screw 110 into a vertebral body. Preferably, socket 118 iscentered over and coaxial with bore 124. Shank 120 includes aself-tapping tip 121.

Screw assembly 100 is pre-assembled with multiple housings thatfacilitate separate locking steps. A lower housing 130 facilitateslocking of screw assembly 100 into channel 250 of plate 200, while stillallowing translation of the screw assembly along the length of thechannel. In one orientation, screw assembly 100 has a range of motionthat allows it to both pivot and translate within channel 250. Inanother orientation within channel 250, screw assembly 100 has arestricted range of motion that only permits it to translate along thelength of the channel. As will be described, screw assembly 110 can betranslated in channel 250 to apply compression to the vertebral bodies.Once the lower housing 130 is locked, an upper housing 140 is operableto lock the position of screw assembly 100 within channel 250 of plate200.

Referring now to FIGS. 3-5, lower housing 130 includes a generallycylindrical body having a central bore 131 that extends through theentire length of the lower housing. A proximal end of lower housing 130has a rounded exterior with opposing flat sides 130 a. A distal end oflower housing 130 includes a rounded seat 137 that cooperatively engagesthe rounded head 112 of polyaxial screw 110. Bore 131 includes an innerthread 133 extending along a section of the bore beginning at theproximal end of lower housing 130 and ending in the area of seat 137.

The exterior of lower housing 130 includes a lower locking flange 134having a profile that generally forms a parallelogram. The parallelogramhas a pair of opposing long sides 134 a, having a dimension “LW”, and apair of opposing short sides 134 b, having a dimension “SW”. One end ofeach long side 134 a intersects a short side 134 b at a rounded corner135 having a relatively small or “sharp” radius of curvature, as seenbest in FIG. 5. The remaining end of each long side 134 a merges into arounded corner 136 having a compound curvature with a graduallyincreasing radius that is larger than the radius of curvature at corners135.

Referring to FIGS. 4A and 4B, lower housing 130 includes a small conicalnotch 138 on one side of the housing, just above flange 134. Notch 138is adapted to connect with an insertion instrument and permit theinsertion instrument to manipulate the screw assembly 100. Morespecifically, notch 138 is configured like a port that allows aninsertion instrument to plug into the side of screw assembly 100 andtranslate the screw assembly along the channel in plate 200, as will bedescribed in more detail below.

Referring now to FIGS. 6A and 6B, upper housing 140 includes aring-shaped body having a central opening 141. Opening 141 has agenerally circular shape with two opposing flat sides 141 a, conformingto the external shape of lower housing 130 at its proximal end. In thisarrangement, the proximal end of lower housing 130 is configured forinsertion through central opening 141 with flat sides 130 a aligned withflat sides 141 a. Flat sides 130 a of lower housing are arranged so asto abut flat sides 141 a of central opening 141 to fix the orientationof upper housing relative to lower housing when the two housings areconnected.

Upper housing 140 has a pair of wing-like projections forming agenerally rectangular upper locking flange 144. Flat sides 130 a, 141 aof lower and upper housings 130, 140 are arranged such that the longdimension of lower locking flange 134 extends in parallel to the longdimension of upper locking flange 144 when the two housings areconnected, as shown in FIG. 2. In the assembled condition, the alignedlower and upper locking flanges 134, 144 form a pair of rail slots 146.Each upper locking flange 144 includes a series of male protrusions,such as small dimples or bosses 145 on the underside of the flange so asto protrude into a rail slot 146 after assembly with lower housing 130.Bosses 145 are incrementally spaced at equal distances in a straightline. In some systems, it may be desirable to arrange the bosses in acurved arrangement to conform to the curvature of the correspondingplate. The spacings and geometry of the bosses are preferably selectedto eliminate micro-movement between the upper housing 140 and plate 200.

Screw assembly 100 is pre-assembled with on-board locking mechanismsthat avoid the need to introduce separate fasteners during surgery. Thiseliminates the need to handle, insert and thread separate fasteners intothe housings, thereby reducing the number of steps during surgery. Anumber of on-board locking elements may be employed, such as torquedriven set screws. Alternatively, a non-torque driven locking elementmay be used, such as any of the locking caps described in U.S. patentapplication Ser. No. 11/753,161, the contents of which are incorporatedby reference herein. Referring again to FIG. 3, the on-board lockingmechanisms used in screw assembly 110 include a lower locking element150 and an upper locking element 160. Lower locking element 150 has agenerally cylindrical body with a central hex socket 151. The bodyincludes a generally flat proximal end 152 and a generally flat distalend 153. The outer edge of lower locking element 150 includes anexternal thread 154. Thread 154 meshes with internal thread 133 in lowerhousing 130, so that the lower locking element can be threaded into bore131 and axially displaced in the bore in response to rotation. In thisarrangement, lower locking element 150 can be driven into bore 131 andtighten polyaxial screw head 112 against seat 137. Screw assemblies usedin accordance with the present invention may include optional insertsfor enhancing the locking engagement between the screw head and seat. Inscrew assembly 100, for example, lower housing 130 includes aring-shaped insert 170 to distribute locking forces more uniformly tothe head 112 of polyaxial screw 110. Insert 170 includes a bore 171 thatforms a passage between respective sockets of screw head 112 and lowerlocking element 150. A proximal end 172 of insert 170 engages lowerlocking element 150, and a distal end 173 of the insert engagespolyaxial screw head 112. Distal end 173 has a concave recess 174 thatconforms to the geometry of at least a portion of screw head 112,forming a contact interface with a substantial portion of the screwhead.

Upper locking element 160 has a generally cylindrical body having aproximal end 162 and a distal end 163. A hex socket 161 extends throughupper locking element 160 from the proximal end to the distal end.Proximal end 162 includes a rimmed cap portion 165 that extends radiallyoutwardly with respect to the remainder of upper locking element 160.Upper locking element 160 is configured for insertion through upperhousing 140 and into bore 131 of lower housing 130 when the upper andlower housings are assembled. The inner diameter of upper housing 140 islarger than the outer diameter of the distal portion of upper lockingelement 160, but smaller than the diameter of rimmed cap portion 165. Asa result, the smaller diameter portion of upper locking element 160 canpass into upper housing 140, while the rimmed cap portion is stopped atthe opening into the upper housing.

An external thread 164 extends along the exterior of upper lockingelement 160 beneath cap portion 165. External thread 164 meshes withinternal thread 133 in lower housing 130, so that upper locking element160 can be threaded into bore 131 and axially displaced in the bore inresponse to rotation. In this arrangement, upper locking element 160 canbe driven into bore 131, and rimmed portion 165 can be tightened againstupper housing 140.

System 10 may include a number of plates having different configurationsand contours to conform to different sections of the spine. For example,plates with a linear or flat longitudinal profile may be used.Alternatively, the plate may feature a curved profile, such as a singlecurvature with one radius, or a compound curvature. System may furtherinclude a set of plates, each with a different radius of curvature orcompound curvature customized to conform with the spinal curvature at aspecific region of the spine. Referring now to FIGS. 7-11, plate 200includes an elongated body 210. Body 210 has a curvature 211 thatgenerally conforms to the lordotic curvature of the spine. Plate 210 hasa proximal end 212 that cooperates with an insertion instrument, and adistal end 218, which is the first section that is inserted into thepatient. Proximal end 212 includes an instrument portal 214 that has arelatively large aperture 215 that receives an end of an insertioninstrument. Aperture 215 is recessed within a portion of proximal end212. A small threaded bore 216 connects aperture 215 with the interiorchannel 250 of plate 210. Portal 214 permits an insertion instrument toengage and manipulate a screw assembly arranged in the plate, as will bedescribed below.

Plate 200 includes a pair of side rails 230 that extend in parallelplanes and interconnect the proximal and distal ends 212, 218. Each siderail 230 has an upper surface 232 and a lower surface 234. Uppersurfaces 232 each feature an angled locking face 236, as seen best inFIG. 11. Locking faces 236 are pitched outwardly and away from thecenter of plate 200. Each locking face 236 has a plurality of smallround recesses 238 arranged in series. Recesses 238 have dimensionsslightly greater than the dimensions of bosses 145 on upper housing 140.In the assembled arrangement, bosses 145 are configured to index withrecesses 238 and detachably couple upper locking flanges 144 to siderails 230, as shown in FIG. 2. Recesses 238 are tightly spaced to permitupper locking flanges 144 to attach to plate 200 at several possiblelocations, and to undergo minor positional adjustments along the lengthof the plate. Each side rail 230 also has a shallow indentation 260extending along the exterior of plate 200. Each indentation 260 forms anupper engagement lip 262 and a lower engagement lip 264. As will bedescribed, indentation 260 and engagement lips 262, 264 cooperate withinstruments to stabilize the plate against rolling or rotation duringsurgical procedures.

Channel 250 is bordered by a pair of inner side walls 252 joined byrounded ends 254. Inner side walls 252 are spaced apart by a channelwidth “W” that is equal to or slightly greater than dimension SW oflower locking flange 134, and smaller than dimension LW of the lowerlocking flange. As such, channel 250 is adapted to receive lower lockingflange 134 by insertion with the lower locking flange oriented with thelong sides generally parallel to side rails 230. Each inner side wall252 has a narrow locking groove 257 extending in the side wall andfollowing the curvature of elongated body 210. Each groove 257 has aheight that is slightly greater than the thickness of lower lockingflange 134 on lower housing 130. In this configuration, lower lockingflange 134 is configured for insertion into locking grooves 257. Toinsert lower locking flange 134 into grooves 257, the lower lockingflange is rotated approximately 90 degrees to pivot short sides 134 binto the grooves. The depths of grooves 257 allow the short sides 134 bto be rotated so that the short sides are completely received in thegrooves and extend parallel to the side rails.

Referring to FIGS. 11A and 11B, a lower housing 130′ and plate 200′ areshown in accordance with alternate embodiments of the invention. Lowerhousing 130′ includes a locking flange 134′ with short sides 134 a′ eachhaving a raised projection 134 b′. Plate 200′ includes a groove 257′with recesses 257 a′ that conform to the raised projections 134 b′. Inoperation, raised projections 134 b′ engage with lateral recesses 257 a′when lower housing 134′ is rotated to the locked orientation to furtherstabilize the lower housing in groove 257′.

Prior to introducing each screw and plate assembly, the position andangular orientation of each pedicle screw is determined. Thepre-determined trajectories of the screw shanks are initially set byguide wires that are driven into the vertebral bodies to mark thepositions and angular orientations of each screw shank. Referring now toFIGS. 12 and 13, an exemplary kit 300 for providing minimally invasiveguidewire insertion is shown in accordance with the invention. Guidewireinsertion kit 300 generally includes an insertion handle 310, a tubularcasing 320 and a guidewire 350 which is loaded into the casing.Guidewire insertion kits in accordance with the invention may includeone or more tubular sections within the casing. In kit 310, casing 320includes an upper tube 322 and a lower tube 328. Upper tube 322 andlower tube 328 are interconnected by a threaded engagement and havebores extending along their respective lengths that align coaxially tofacilitate insertion of guidewire 350 as shown. Lower tube 328 has adistal end 331 forming a conical taper 332 for percutaneous insertionthrough tissue. Distal end 331 may have a number of contact surfaces,such as a serrated edge, to engage bone and prevent slippage when casing320 is in contact with the bone. The bore in lower tube 328 includes aconstriction having an inner diameter generally equal to the diameter ofguidewire 350 so as to frictionally engage the guidewire. As with otherinstruments, components of guidewire insertion kit 300 may be formed ofradiolucent material so that guidewire placement can be more clearlymonitored under imaging.

Insertion handle 310 includes a gripping end 312 for holding theassembled tubes 322, 328 in position, and a holder end 314. Holder end314 has a tubular ring 315 that is clamped around the upper tube 322. Aball plunger 316 that extends partially within ring 315 provides africtional coupling between handle 310 and casing 320. A generallycylindrical slide hammer 326 is slidably displaceable around upper tube322. A blind bore extends through a bottom end of slide hammer 326 andterminates inside a mid-region of the slide hammer. In operation, slidehammer 326 is lifted upwardly or proximally along the upper tube andreleased. The slide hammer 326 falls by gravity until the end of theblind bore in the slide hammer contacts the proximal end of the uppertube 322. The lifting and dropping is done repeatedly to gradually driveguidewire 350 into the vertebral body. The position and orientation ofguidewire 350 may be monitored as it is driven into the bone using anumber of imaging techniques. The upper and lower tubes 322, 328 areconfigured for removal from guidewire 350 once the guidewire position isset. Preferably, guidewire 350 is slightly longer than casing 320.

The tissue immediately surrounding the inserted guidewires 350 may bedilated using a number of different dilation tools. FIGS. 14 and 15illustrate an exemplary dilator sleeve 400 and dilator tip 410. Dilatorsleeve 400 and tip 410 may be advanced over a guidewire 350 and driveninto the tissue surrounding the guidewire to dilate the tissue. In apreferred embodiment, dilator sleeve 400 and tip 410 are configured tobe advanced over casing 320 of the guidewire insertion kit, so that thecasing does not have to be removed prior to dilation. A variety oftissue dilation components may be used in accordance with the invention,including components that are interchangeable or otherwise compatiblewith the guidewire insertion kit 300.

Referring back to FIGS. 7 and 8, plate 200 is configured to be insertedpercutaneously through tissue and positioned around guidewires 350 afterthe guidewires are set. Percutaneous insertion of plate 200 is done in aminimally invasive manner that minimizes the trauma to the tissue andblood vessels. This is facilitated in part by body 210, which has arelatively small thickness and width, forming a smooth narrow profile.Distal end 218 of plate 200 has a rounded nose portion 220 that smoothlynavigates through tissue during insertion. Nose portion 220 has a split222 that extends from the outer perimeter of body into channel 250. Anouter portion of split 222 opens out into V-shaped notch 224. Split 222and V-notch 224 allow plate 200 to be passed over each guidewire.V-shaped notch 224 is adapted to capture each guidewire and draw theguidewire inwardly toward the center of split 222. The width of split222 is preferably slightly smaller than the diameter of guidewire 350 sothat the guidewire abuts the nose portion at the location of the split.The relatively long dimension of plate body 210, and the relativelynarrow profile of side rails 230 allow the nose portion to flex apart atthe split in response to contact with guidewire 350. In thisarrangement, guidewire 350 can be wedged through split 222 and enterchannel 250 when plate 200 is driven against the guidewire. Nose portion220 is resiliently flexible, allowing the nose portion to snap over theguidewire and close the split once the guidewire passes into channel250. The abutment between guidewire 350 and nose portion 220, followedby the opening of the nose portion at split 222 and passage of theguidewire through the split, are associated with different levels ofresistance that offer a tactical aid to the surgeon during positioningof the plate. Specifically, the resistance presented by plate 200against passage of each guidewire 350, and the subsequent release ofeach guidewire from split 222 into channel 250, are sensed by thesurgeon through inserter instrument to alert the surgeon that eachguidewire has successfully entered the plate channel.

Referring now to FIG. 16, an exemplary plate orientation assembly 500 isshown in accordance with one embodiment of the invention. Plateorientation assembly 500 includes components that cooperate with oneanother to properly orient plate 200 with respect to guidewires 350 andthe intended screw orientations. The term “plate orientation” broadlyencompasses a number of positional adjustments of the plate. Theseadjustments include centering plate 200 with respect to each guidewire350 so that the guidewire intersects a centerline passing through thelong axis of the plate (hereinafter, “plate centering”). In addition,proper orientation of plate 200 includes canting or tilting the plate sothat the plane of the guidewire 350 is generally parallel to thesidewalls of the channel 250 (hereinafter, “plate angling”). Forpurposes of this description, the process of drawing the plate into aperpendicular relationship with the each screw assembly will be treatedas a separate step referred to as “plate reduction.”

Plate orientation assembly 500 includes two primary instruments: anobturator 510 and a plate reduction sleeve 550. Obturator 510 isconfigured for insertion into a bore extending through plate reductionsleeve 550, and operates as a unit with the plate reduction sleeveduring plate orientation. Obturator 510 is used for plate centering andplate angling. Plate reduction sleeve 550, as the name implies, is usedfor plate reduction. By achieving plate centering and plate angling,obturator 510 prepares plate 200 for engagement with plate reductionsleeve 550. Although obturator 510 and plate reduction sleeve 550cooperate and function together during plate orientation, each componentcan also operate on its own, and can be used for purposes other thanplate orientation. For example, plate reduction sleeve also functionswithout obturator as a surgical portal and counter-torque applicatorduring insertion of the screw assembly, as will be described insubsequent sections.

Referring now to FIGS. 17-22, obturator 510 will be described inadditional detail. Obturator 510 includes a hollow cylindrical body 512and a rounded probe end or tip 516 that projects from the distal end ofbody 512. Obturator tip 516 has a straight section 517 and a tapered end518. Tapered end 518 is narrow enough to be inserted into channel 250 ofplate 200 at any orientation. Straight section 517, however, has across-sectional profile that can only be inserted into channel 250 incertain specific orientations. Straight section 517 has a rounded crosssection with opposing flat sides 517 a and rounded ends 517 b, as shownin FIG. 20. The minimum width of straight section 517 is “W_(min)”,extending between flat sides 517 a. The maximum width of straightsection 517 is “W_(max)”, extending between rounded ends 517 b andperpendicular to W_(min). W_(min) is more or less equal to the width ofchannel 250, and increases around the perimeter of straight section 517.In this arrangement, straight section 517 can only enter and passthrough channel 250 with flat sides 517 a aligned parallel to side walls256 of the channel. Sidewalls 256 are adapted to engage flat sides 517 aand substantially prevent rotation of tip 516 in channel 250. Obturatortip 516 is permitted to translate and tilt within channel 250, in aplane parallel to the sidewalls of the channel.

Obturator 510 includes a locking mechanism to detachably connectorientation assembly 500 with plate 200. A number of locking mechanismscan be used in accordance with the invention. Referring to FIG. 19, thelocking mechanism includes a pair of resilient locking springs 536.Locking springs 536 are radially displaceable between a retractedcondition, in which the locking springs are positioned within obturatortip 516, and an expanded condition, in which the locking springs projectradially outside of the obturator tip. Each locking spring 536 includesa spring tab 538 that extends radially outwardly from the lockingspring. Obturator tip 516 includes a pair of diametrically opposed tabslots 520 that are radially and axially aligned with locking springs 536to allow the locking springs, or at least spring tabs 538, to projectoutwardly through the slots. In the expanded condition, the axialdistance between each spring tab 538 and the distal end of body 512, asshown for example in FIG. 19, is generally equal to or slightly largerthan the height of plate 200 (i.e. the dimension between the upper andlower surface of plate 200).

In the relaxed condition, locking springs 536 are in the retractedposition, with spring tabs 538 recessed in the interior of obturator tip516. Locking springs 536 are displaceable from the retracted position tothe expanded condition in response to rotation of an inner shaft 522extending within obturator tip 516. Inner shaft 522 has a cam end 524which is operable to move locking springs 536 between the retracted andexpanded conditions. Referring to FIGS. 21 and 22, cam end 524 has apair of opposing indents 525 and a pair of opposing lobes 526 offsetfrom the indents by 90 degrees. Indents 525 are adapted to receivelocking springs 536 in the retracted condition. In contrast, lobes 526are configured to push locking springs 536 radially outwardly to theexpanded position upon rotation of cam end 524. In this arrangement,locking springs 536 can be toggled between the expanded condition andretracted condition in response to rotation of inner shaft 522 and camend 524. Inner shaft 522 is connected to a plunger 527 that extends tothe proximal end of obturator 510. At the proximal end of obturator 510,plunger 527 is press fitted into a control knob 532. Control knob 532 isrotatable relative to obturator body 512. In this configuration, cam end524 can rotate in response to rotation of control knob 532 to move thelocking springs 536 between the retracted condition and the expandedcondition.

The axial position of obturator tip 516 relative to body 512 isseparately controlled by a body cap 528. Body cap 528 is coupled tocontrol knob 532 by a C-ring 531 or similar coupling. The outercircumference of body cap 528 has an external thread 530 that engages aninner thread 513 inside obturator body 512. In this arrangement, bodycap 528 is rotatable along the threaded engagement to axially displacecontrol knob 532, plunger 527, inner shaft 522 and obturator tip 516relative to body 512. C-ring 531 allows body cap 528 to rotateindependently from control knob 532, and limits the transfer of torquefrom the body cap to the control knob and plunger 527.

In the preferred embodiment, the obturator includes markings or indiciato provide a visual indication of whether the spring tabs are in theretracted or “unlocked” condition, or in the expanded or “locked”condition. In FIGS. 17 and 18, for example, body 512 includes a firstindicia 512 a in the form of a line and a second indicia 512 b in theform of a line, the second indicia being generally parallel to andangularly offset from the first indicia. Control knob 532 has a thirdindicia 532 a that can be rotated into alignment with one of the firstand second indicia 512 a, 512 b. When third indicia 532 a is alignedwith first indicia 512 a, cam end 524 is oriented so that spring tabs538 are retracted into obturator tip 516. When third indicia 532 a isaligned with second indicia 512 b, cam end 524 is oriented so thatspring tabs 538 are expanded outwardly through slots 520. In thisarrangement, alignment with first indicia 512 a is indicative of anunlocked mode, and alignment with second indicia 512 b is indicative ofa locked mode.

Control knob 532, plunger 527, inner shaft 522 and obturator tip 516 arecannulated and have bores that align coaxially or substantiallycoaxially with the longitudinal axis of obturator body 512. The borescollectively form a passage for a guidewire, such as guidewire 350.Obturator 510 is configured to be advanced over an implanted guidewire350 and into channel 250 of plate. As will be explained below, obturator510 is operable to properly orient plate 200 relative to each guidewire350 prior to introducing screw assemblies 100 into the plate. Althoughplate 200 is properly centered and parallel with respect to eachguidewire 350, the guidewire may not extend normal to the plate. As aresult, a screw assembly 110 that is advanced down guidewire 350 intochannel 250 may not enter the channel with upper and lower lockingflanges oriented in the proper planes to engage the plate. In such acase, lower locking flange 134 will enter channel 250 in a plane that isnon-parallel to the adjacent grooves 257 in sidewalls 256. To correctfor the misalignment, orientation assembly 500 is operable to reduce ordraw plate 200 into proper alignment with the guidewire orientationprior to introducing a screw assembly. This alignment of plate 200 isaccomplished with plate reduction sleeve 550.

Referring now to FIGS. 23-27, plate reduction sleeve 550 will bedescribed in more detail. Among other functions, plate reduction sleeve550 is operable to reduce or draw plate 200 into a position that isnormal to the centered guidewire 350, and retain the plate in thatposition. With the guidewire 350 centered in channel 250 and retainednormal to plate 200, a screw assembly 100 can be properly locked intoplate 200. Plate reduction sleeve 550 includes a generally cylindricalouter shaft 552 and a generally cylindrical inner shaft 570 extendingwithin the outer shaft. Inner shaft 570 is interconnected to outer shaft552 by an adjustment knob 590 attached at the proximal ends of the innerand outer shafts. As will be discussed, inner shaft 570 is axiallydisplaceable within outer shaft 552, but can not rotate relative to theouter shaft.

Outer shaft 552 includes a hollow body 554 forming a bore 555, as shownin FIGS. 25 and 26. Body 554 includes a pair of diametrically opposedguide arms 567 that are cut out from the sidewall of bore 555. Eachguide arm 567 includes a tab 567 a that extends radially inwardly intobore 555 of outer shaft 552. Guide arms 567 are resiliently flexible. Ina relaxed condition, guide arms 567 extend along body 554 with tabs 567a projecting radially inwardly inside bore 555. A proximal end 556 ofouter shaft 552 includes a locking ring 558 for retaining adjustmentknob 590 in a rotatable coupling. Proximal end 556 also includes anengagement surface 566 for instrumentation, such as for example, acounter torque instrument. A distal end 560 of outer shaft 552 includesa pair of distal extensions 562. Distal extensions 562 form a pair ofarcuate notches in body 554 that collectively form a plate socket 564.Preferably, the notches forming plate socket 564 have a geometry thatconforms with the shape of the upper surface of plate 200.

Referring now to FIGS. 27 and 28, inner shaft 570 includes a hollow body571 configured for insertion into bore 555 of outer shaft 552. Body 571includes a pair of diametrically opposed guide slots 580. Guide slots580 are axially positioned to align with guide arms 567 in outer shaft552 when inner shaft 570 is inserted into outer shaft. Tabs 567 a extenda sufficient distance within bore 555 so as to engage the exterior ofinner shaft 570 as the inner shaft is inserted into outer shaft 552.Guide arms 567 have sufficient flexibility to bend outwardly from thewall of outer shaft 552. In this arrangement, engagement of tabs 567 awith the outer wall of inner shaft 552 displaces guide arms 567 radiallyoutwardly until guide slots 580 align with the tabs. Upon alignment withguide slots 580, the deflected guide arms 567 snap inwardly such thatguide tabs 567 a enter the slots 580 to connect the inner and outershafts together. Tabs 567 a are confined within slots 580 and arepermitted to move axially relative to inner shaft 570. The sidewalls ofslots 580 engage with the tabs to prevent rotation of inner shaft 570relative to outer shaft 552.

Inner shaft 570 is axially displaced within outer shaft 552 byadjustment knob 590. Referring to FIG. 29, adjustment knob 590 includesan inner thread 592 that engages an external thread 574 on proximal end573 of inner shaft 570 when plate reduction sleeve 550 is assembled.Adjustment knob 590 also includes a rim 594 that cooperatively engageslocking ring 558 on a proximal end 556 of outer shaft 552. Rim 594slidably engages locking ring 558 to allow rotation of knob 590 relativeto outer and inner shafts 552, 570. The walls in locking ring 558substantially limit axial movement of knob 590 relative to outer shaft552, however. In this arrangement, adjustment knob 590 and outer shaft552 are axially displaceable in unison relative to inner shaft 570 whenthe knob is rotated along the threaded engagement between the knob andinner shaft.

A distal portion of inner shaft 570 includes pair of diametricallyopposed flex arms 577. Each flex arm 577 includes a clamping member 578that extends radially outwardly from the rest of the flex arm, as shownin FIG. 28. Clamping members 578 are arranged on the circumference ofinner shaft 570 so as to radially align with distal extensions 562 onouter shaft 552 when the inner shaft is inserted into the outer shaft.The cross sectional width of inner shaft 570 at clamping members 578 islarger than the inner diameter of bore 555 between distal extensions 562of outer shaft 552. Flex arms 577 and clamping members 578 are axiallydisplaceable relative to outer shaft 552 in response to rotation ofadjustment knob 590. In particular, clamping members 578 aredisplaceable between a clamping mode, in which the clamping members aredrawn into outer shaft 552, and a release mode, in which the clampingmembers extend more outwardly from the outer shaft. Clamping members 578are configured to deflect radially inwardly toward one another withminimal resistance upon being moved to the clamping mode in outer shaft552. Each clamping member 578 includes a small ramp portion 578 aforming a camming surface that contacts the distal end of outer shaft552 during retraction of the clamping members into the outer shaft. Rampportions 578 a are pitched so as to direct radially inward components offorce on clamping members 578 during retraction into outer shaft 552.Each clamping member further includes an inwardly extending detent 580and an inner gripping surface 582. As will be discussed, detents 580 andinner gripping surfaces 582 are configured to engage side rails 230 ofplate 200 to facilitate reduction of the plate.

Proximal end 573 of inner shaft 570 includes a pair of diametricallyopposed indexing slots 584 that cooperate with alignment mechanisms onother instruments inserted into plate reduction sleeve 550. Indexingslots 584 permit insertion of certain instruments in certainorientations so as to maintain proper alignment between the insertedinstruments, the plate 200 and the screw assembly 100. Indexing slots584 may be used to align a number of instruments, including componentsof a counter-torque kit which will be described in more detail below.

Obturator 510 and plate reduction sleeve 550 are interconnected andindexed with one another in a releasable engagement. Obturator body 512includes a pair of resilient indexing detents 514 with detent ends 514 athat project radially outwardly from the detents. Inner shaft 570 ofplate reduction sleeve 550 has a corresponding pair of slots 579 thatare aligned with detents 514 on obturator body 512 when obturator 510 isinserted into plate reduction sleeve 550. Upon insertion of obturator510 into plate reduction sleeve and alignment of detents 514 with slots579, detent ends 514 a snap into the slots, producing an audible clickthat indicates that the components of plate orientation assembly 500 areassembled. The assembled plate orientation assembly 500 can then beadvanced over a guidewire 350 to begin plate orientation. The differentsteps of plate orientation will be described in more detail in thesections focusing on the operation of the assembly 10.

Referring now to FIGS. 30 and 31, a screw housing manipulator 600 isshown in accordance with one exemplary embodiment of the presentinvention. Screw housing manipulator 600 works as a carrier for screwassemblies 100. In particular, screw housing manipulator 600 can beloaded with a screw assembly 100 during preparation for surgery, andsubsequently advanced over a guidewire 350 through a plate reductionsleeve 550 to introduce the screw assembly into a plate 200. Screwhousing manipulator 600 includes an inner shaft 610 that istelescopically inserted in an outer shaft 640. A handle 616 is connectedto a proximal end 612 of inner shaft 610. Inner shaft 610, which isshown in more detail in FIGS. 32-34, includes a distal end 614 with apair of diametrically opposed flexible arms 620. Each flexible arm 620has a clamping extension 622 that extends distally from the flexible armand serves as a gripping element for engaging a screw assembly 100.Handle 616 is operable to rotate and lock a screw assembly 100 into aplate 200, as will be discussed in more detail.

Referring now to FIGS. 35 and 36, outer shaft 640 of screw housingmanipulator 600 includes a proximal end 642 having a retaining ring 646,and a distal end 644. Outer shaft 640 is generally cylindrical, forminga bore 645 that extends through the length of the outer shaft. Thediameter of bore 645 is adapted to receive inner shaft 610 and slidablyengage the inner shaft in a fixed orientation relative to the outershaft. Inner shaft 610 includes a small longitudinal slot 628, and outershaft 640 includes a small longitudinal slot 652 that aligns with theslot of the inner shaft. Slots 628, 652 are adapted to receive a pin 660that extends through both slots to lock the relative orientation ofinner shaft 610 with respect to the orientation of the outer shaft 640.

Inner and outer shafts 610, 640 are coupled to one another by controlcollar 670. Referring now to FIG. 37, control collar 670 is generallycylindrical and forms a central bore 672. Bore 672 includes an innerthread 674 that engages an external thread 618 on inner shaft 610. Bore672 also includes a socket portion 675 forming an annular groove 676.Groove 676 receives a flange 647 on retaining ring 646 to interconnectcollar 670 to the retaining ring. The threaded engagement between collar670 and inner shaft 610 permits the collar to be axially displaceablealong inner shaft 610. In contrast, the flange and groove connectionbetween collar 670 and outer shaft 640 permits rotation of the collarrelative to the outer shaft but substantially prevents axialdisplacement of the collar relative to the outer shaft. In thisarrangement, control collar 670 is rotatable to axially advance innershaft 610 relative to outer shaft 640 in a telescoping arrangementwithin bore 645.

Collar 670 is operable to displace flexible arms 620 between a clampingposition, in which the arms are drawn proximally into outer shaft 640,and a release position, in which the arms are extended distally relativeto the clamping position. In a relaxed condition, the distance betweenthe outer surfaces of flexible arms 620 is slightly larger than theinner diameter of bore 645 in outer shaft 640. In this arrangement, theinner wall of bore 645 is configured to compress the flexible arms 620inwardly and toward one another as the arms are drawn to the clampingposition in outer shaft 640. Referring to FIGS. 33 and 34, each clampingextension 622 forms a bell-shaped socket 624 and a clamping tab 626 atthe distal-most end of the clamping extension. Bell-shaped sockets 624have an internal geometry that conforms with the geometry of upperhousing 140 in screw assembly 100. Referring back to FIG. 6 a, upperhousing 140 has a curved shape that conforms with a curvature 625 ineach bell-shaped socket 624. Upper housing 140 also includes a pair ofopposing gripping slots 142, one on each side of upper locking flange144. Gripping slots 142 are diametrically opposed with one another in asymmetrical arrangement and align radially with clamping tabs 626 inscrew housing manipulator 600.

Referring again to FIG. 31, screw housing manipulator 600 is configuredfor insertion into plate reduction sleeve 550 to introduce a screwassembly 100 to plate 200. The orientation of screw assembly 100relative to plate 200 is preferably controlled to ensure that the screwassembly, and particularly lower and upper housings 130, 140, enter theplate channel 250 in the correct orientation. To this end, theorientation of screw assembly 100 relative to plate 200 and platereduction sleeve 550 is controlled by an indexing arrangement. Outershaft 640 of screw housing manipulator 600 includes pair of flexibleindexing tabs 648. Indexing tabs 648 each have a tab end 650 thatextends radially outwardly from screw housing manipulator 600. Tab ends650 register with a pair of diametrically opposed receiver slots 586 ininner shaft 570 of plate reduction sleeve 550, the slots being shown inFIGS. 27 and 28. The engagement between tab ends 650 and receiver slots586 permit screw housing manipulator 600 to slide axially relative toplate reduction sleeve 550, but prevents the screw housing manipulatorfrom rotating relative to the plate reduction sleeve.

Inner shaft 610 of screw housing manipulator 600 is hollow and forms apassage 611. Passage 611 extends along the longitudinal axis of screwhousing manipulator 600, passing through handle 616. In thisarrangement, passage 611 provides access to a screw assembly 100 afterscrew housing manipulator 600 is inserted into plate reduction sleeve550. As will be discussed, the pedicle screw head 112, lower lockingelement 150, and upper locking element 160 in screw assembly 100 are allconfigured to cooperate with different sized drivers. Passage 611provides one common axis portal for all the drivers.

Application of torque to the screw head and locking elements,particularly lower locking element 150, can require a substantial amountof torque. Preferably, the transfer of torque to plate 200 is eliminatedor minimized. This can be accomplished in a number of ways. Referringnow to FIGS. 38-41, exemplary components of a counter-torque kit areshown in accordance with the invention. The counter-torque kit is usedto stabilize plate 200 and fix the plate against rotation as the lockingelements within the screw assembly are tightened. Plate stabilization isaccomplished with three components: a stabilization sleeve 710, theplate reduction sleeve 550 previously described, and a counter-torquehandle 730 that applies counter force to the plate reduction sleeve.

Stabilization sleeve 710 is configured for insertion into platereduction sleeve 550 to stabilize the position of plate 200 from insidechannel 250. Sleeve 710 includes a proximal end 712 featuring a knob713, and a distal end 714 with a pair of stabilizing plates 716. Eachstabilizing plate 716 has a plate width “W_(p)” substantially equal tothe width of channel 250 in plate 200. Stabilization sleeve 710preferably includes an alignment mechanism that ensures that the sleeveis in the correct orientation to permit insertion of stabilizing plates716 into channel 250. In the illustrated embodiment, proper alignment isfacilitated by using the orientation of plate reduction sleeve 550 as abasis for setting the orientation of stabilization sleeve 710. Indexingslots 584 in plate reduction sleeve 550 are adapted to receive a pair ofdiametrically opposed projections 718 that extend radially outwardlyfrom sleeve 710. Each projection 718 has a width that is equal to orslightly less than the width of indexing slots 584. The maximum widthacross projections 718 is greater than the inner diameter of platereduction sleeve 550. In this arrangement, stabilization sleeve 710 canonly be inserted into plate reduction sleeve 550 with projections 718aligned with indexing slots 584. Projections 718 are also alignedradially with stabilizing plates 716. In this arrangement, stabilizationsleeve 710 can only be inserted into plate reduction sleeve 550 withstabilizing plates 716 oriented perpendicularly to the longitudinaldirection of plate 200. As such, the stabilizing plates are in properalignment to be inserted into channel 250 without the need forrotational adjustment.

Referring next to FIGS. 40 and 41, counter-torque handle 730 includes ahead 732 connected with a handle assembly 740. Head 732 includes a baseportion 734 for attachment with handle assembly 740 and a curvedextension 736. Curved extension 736 has a first plug 738 that extendsinwardly relative to the curvature of the extension. Handle assembly 740includes a handle body 742 for gripping the counter-torque handle 730and a central bore 744. An elongated rod 746 is axially displaceable inbore 744 between an extended position to lock the counter-torque handle730 to an article and a retracted position to release the counter-torquehandle from an article. In the extended position, rod 746 projectsoutwardly from base portion 734 in an exposed manner to adjacent curvedextension 736. The exposed portion of rod 746 forms a second plug 748,as shown in FIG. 40. Together, first plug 738 and second plug 748 form asecure coupling with a counter-torque engagement surface.

A biasing spring 752 circumscribes the rod near the proximal end ofhandle body 742. A first end of spring 752 bears against an inner cap754 in the proximal end of handle body 742, and a second end of spring752 bears against an enlarged midsection 750 of rod 746. Spring 752 iscompressed between inner cap 754, which is fixed relative to handle body742, and midsection 754 of rod 746, which is axially displaceablerelative to the handle body. In this arrangement, stored energy inspring 752 biases rod 746 toward the extended or locking position. Apull knob 756 attached to rod 746 is operable to draw the rod proximallyagainst the bias of spring 752 toward the retracted position.

Counter-torque handle 730 is configured to engage a counter-torquesurface on plate reduction sleeve 550. Referring again to FIGS. 23-26,outer shaft 552 of plate reduction sleeve 550 is circumscribed byengagement surface 566. Engagement surface 566 includes an arrangementof holes 568 incrementally spaced at equal distances from one anotheraround the circumference of outer shaft 552. The arc length betweenfirst plug 738 and second plug 748 generally corresponds to the arclength between two of holes 568. In this arrangement, any two holes 568are adapted to receive first plug 738 and second plug 748 when curvedextension engages engagement surface 566.

Referring now to FIGS. 42 and 43, an inserter instrument 1000 for usewith the spinal stabilization system 10 is shown in accordance with oneexemplary embodiment of the invention. Inserter 1000 can be used toinsert plate 200 through an incision and position the plate above two ormore vertebral bodies to be stabilized. Inserter 1000 is also operableto adjust the relative position of screw assemblies 100 within platechannel 250. Adjustment of the screw assemblies 100 is done with a verysmall probe that penetrates through an end of plate 200 and into platechannel 250 where it engages the screw assembly to be adjusted. Morespecifically, the small probe passes through portal 214 in plate 200,and engages notch 138 on the side of screw assembly 100. With thisarrangement, inserter 1000 allows the screw assemblies 100 to beadjusted remotely with minimally invasive procedures. Adjustment of thescrew assemblies 100 can be performed to adjust the position of thevertebral bodies, and apply compression or decompression to the discspace (depending on direction of movement).

Inserter 1000 is generally elongated in shape and includes a proximalend 1002, having a handle assembly 1004, and a distal end 1006, having aflexible shaft assembly 1008. A longitudinal axis 1010, extendsgenerally between proximal end 1002 and distal end 1006. Flexible shaftassembly 1008 is configured to extend in a distal/proximal directionrelative to handle assembly 1004 generally along longitudinal axis 1010,and to also rotate about longitudinal axis 1010. Flexible shaft assembly1008 is generally cylindrically shaped, with a distal tip 1112 thatcurves away from longitudinal axis 1010. Flexible shaft assembly 1008includes an inner shaft 1009 slidably disposed within an outer shaft1011, as shown in FIG. 44.

Referring to FIGS. 43 and 44, handle assembly 1004 includes a handlebody 1014 fixedly coupled to a handle grip assembly 1016. Handleassembly 1004 includes a handle body 1014 and a handle cover 1017releasably coupled to handle body 1014, such as by threaded fasteners1018. Handle grip assembly 1016 includes a contoured grip 1020 having aplurality of ridges to facilitate tactile feel. Grip 1020 may beconstructed from polyetherether ketone (PEEK) or some other suitablematerial. In an exemplary embodiment, a pin 1022 may be inserted throughgrip 1020 and into handle grip assembly 1016, such as with aninterference fit, to secure contoured grip 1020 to handle grip assembly1016. Handle body 1014 houses and maintains the mechanism used both toextend and retract flexible shaft assembly 1008 and to rotate flexibleshaft assembly 1008 about longitudinal axis 1010. Referring to FIG. 45,handle body 1014 includes a generally key-shaped slot 1026 that housesthe mechanism to extend and retract flexible shaft assembly 1008 and agenerally rectangular slot 1027. Rectangular slot 1027 provides accessto a mechanism that rotates flexible shaft assembly 1008 aboutlongitudinal axis 1010.

Referring back to FIGS. 43 and 44, a rack 1028 and a pinion 1030 arehoused within handle body 1014 and cooperate to advance and retractflexible shaft assembly 1008 along longitudinal axis 1010. Pinion 1030is coupled to a first end 1032 a of a pinion shaft 1032. A second end1032 b of pinion shaft 1032 is generally square in cross section. A gearhandle assembly 1034, shown in FIG. 46, which is used to rotate pinion1030, is coupled to the second end 1032 b of pinion shaft 1032. Teeth1033 on pinion 1030 engage teeth 1035 on underside of rack 1028 toadvance and retract rack 1028 along longitudinal axis 1010.

Referring now to FIGS. 44, 47, and 48, rack 1028 is biased towards aproximal position by a biasing element in the form of a helical spring1036. Pinion 1030 is used to advance rack 1028 in a distal direction,against the force of helical spring 1036. A ratchet lever 1038 is usedto maintain rack 1028 in a distal position as pinion 1030 advances rack1028 distally. Rack 1028 includes a cavity 1037 that receives andengages a proximal end of inner shaft 1009. Ratchet lever 1038 includesratchet teeth 1040 that engage corresponding ratchet teeth 1042 on rack1028. Ratchet lever 1038 is coupled to handle body 1014 via a pivot pin1044. A leaf spring 1046 biases distal end of ratchet lever 1038 awayfrom handle body 1014, pivoting ratchet teeth 1040 about pivot pin 1044into engagement with ratchet teeth 1042 of rack 1028. In thisarrangement, ratchet lever 1038 provides a lock that substantiallyprevents the rack and flexible shaft from reversing or moving in aproximal direction under the spring bias. Proximal end of ratchet lever1038 includes a finger grip 1048 that, when depressed toward handle body1014, disengages ratchet teeth 1040 on the ratchet lever from ratchetteeth 1042 on the rack 1028, allowing the rack and flexible shaft 1008to retract in a proximal direction under the bias of the spring.

Referring to FIGS. 44 and 49-52, flexible shaft assembly 1008 alsoincludes an inserter knob 1060 that rotates flexible shaft assembly 1008about longitudinal axis 1010. Inserter knob 1060 includes an annularbody having a plurality of ridges 1062. Ridges 1062 provide a tactilegrip for a user to rotate inserter knob 1060 about longitudinal axis1010. Inserter knob 1060 includes a generally hexagonal inner perimeter1061 that slides over a sleeve 1064. Inserter knob 1060 also includes athreaded slot 1066 that extends through the knob, passing partiallythrough hexagonal inner perimeter 1061 and ending prior to exiting outersurface of inserter knob 1060. Sleeve 1064 includes a complementary,albeit unthreaded, slot 1068 through an outer periphery thereof. A screw1070 extends through threaded slot 1066 and unthreaded slot 1068 tosecure inserter knob 1060 to sleeve 1064. Sleeve 1064 includes ahexagonal proximal portion 1063 that mates with hexagonal innerperimeter 1061, as shown in FIG. 50, and a circular distal portion 1065.Screw 1070 engages outer shaft 1011 such that rotation of inserter knob1060 about longitudinal axis 1010 also rotates outer shaft 1011 aboutlongitudinal axis 1010.

Referring to FIG. 44, proximal end of flexible shaft assembly 1008 isdisposed within a passage 1072 of handle body 1014 such that proximalend of inner shaft 1009 engages cavity 1037 in rack 1028. Proximal endof outer shaft 1011 engages helical spring 1036 to impart biasing forceagainst rack 1028.

Referring now to FIGS. 42 and 53-57, flexible shaft assembly 1008includes an inserter shaft 1080 that is positioned around outer shaft1011 and inner shaft 1009. In FIG. 54, proximal end of inserter shaft1080 includes a pair of spaced-apart, circular ridges 1082, 1084. Aretaining ring 1086 is disposed between ridges 1082, 1084 and extendspartially beyond ridges 1082, 1084. A tapered knob 1088 is slid overinserter shaft 1080 from its distal end toward the proximal end. Taperedknob 1088 includes a circumferential channel 1090, which accepts theportion of retaining ring 1086 that extends beyond ridges 1080, 1084,securing tapered knob 1088 to inserter shaft 1080. Tapered knob 1088includes internal threads 1092 that engage external threads 1093 ondistal end of handle body 1014 (shown in FIG. 44). Referring now toFIGS. 53, 56 and 57, distal end of inserter shaft 1080 includes aninserter tip 1094. Inserter tip 1094 includes a through-passage 1095that allows inner shaft 1009 and outer shaft 1011 to extendtherethrough. Inserter tip 1094 has a pair of diametrically opposeddistal protrusions 1096 and a pair of diametrically opposed proximalprotrusions 1098. Protrusions 1096, 1098 securely engage the proximalend 212 of plate 200 to substantially prevent twisting or rotating ofthe plate with respect to inserter 1000 during insertion. Distalprotrusions 1096, 1098 are asymmetrical, forming a generally invertedU-shaped plug that conforms to the shape of aperture 215 in plate 200.In this arrangement, the distal end of inserter 1000 can only engageplate 200 in one orientation, preventing the user from inadvertentlyengaging the plate with the instrument in the wrong position.

Referring to FIGS. 58-60, outer shaft 1011 is shown. A distal end 1100curves away from longitudinal axis 1010 by an angle α. In an exemplaryembodiment, angle α is about 40°. Proximal end 1104 of outer shaft 1011is coupled to interior of sleeve 1064 as described above. Distal tip1102 includes a tip fitting 1106, shown in detail in FIGS. 59 and 60,that is permanently attached to distal tip 1102 of outer shaft 1011. Tipfitting 1106 includes exterior threads 1108 that engage threaded bore216 in proximal end 212 of plate 200. Tip fitting 1106 includes athrough passageway 1107 to allow inner shaft 1009 to pass therethrough.

Referring now to FIGS. 61-65, inner shaft 1009 is preferably constructedfrom a solid cylinder having a distal end 1109 that curves away fromlongitudinal axis 1010 with the same angle α as described above withrespect to outer shaft 1011. Proximal end 1110 includes a cylindricalprong 1112 that fits into cavity 1037 of rack 1028.

An inner tip fitting 1114 is coupled to distal end 1108 of inter shaft1009. Inner tip fitting 1114 includes a frustoconical distal tip 1116and a cylindrical proximal opening 1118 that is sized to accept a distalprong 1109 extending from distal end 1108 of inner shaft 1009.

Like other instruments and assemblies in accordance with the invention,the inserter instrument 1000 and its parts may be manufactured using avariety of materials. In an exemplary embodiment, pin 1022 may beconstructed from 303 stainless steel and leaf spring 1046 may beconstructed from stainless steel. Additionally, retaining ring 1086,outer shaft 1011, and inner shaft 1009 may all be constructed fromstainless steel. Also, in an exemplary embodiment, handle body 1014,handle cover 1017, rack 1028, pinion 1030, pinion shaft 1032, inserterknob 1060, sleeve 1064, inserter shaft 1080, tapered knob 1088, insertertip 1094, tip fitting 1106, and inner tip fitting 1114 may all beconstructed from precipitation hardening stainless steel, such as 17-4PH™ stainless steel.

The foregoing assemblies and instruments may be used in a number ofsurgical techniques in accordance with the invention. In the sectionsbelow, a general description of a surgical procedure will be provided,followed by a description of how individual instruments and assembliesare operated.

Referring now to FIG. 65, a general outline of one possible procedure2000 in accordance with the invention is shown. For purposes of thisdescription, the procedure will be described with reference toassemblies and instruments described in the sections above. It will beunderstood, however, that the techniques described in this section arenot limited to the assemblies and instruments described in the abovesections. In addition, it will be understood that procedure 2000 is ageneral description that may be supplemented with other steps withoutdeparting from the invention. Furthermore, the sequence of stepsillustrated in FIG. 65 is exemplary only and does not represent the onlycontemplated sequence of steps that may be performed.

A plate may contain two or more screw assemblies, and consequently twoor more guidewires. For purposes of FIG. 65 and the subsequentdescriptions provided below, it will be assumed that the plate containstwo screw assemblies: a first or distal screw assembly, and a second orproximal screw assembly. The term “first” refers to the screw orguidewire position that is farther away from the insertion instrumentattached to the plate, and closer to the split end of the plate. Theterm “second” refers to the screw or guidewire position that is closerto the insertion instrument attached to the end of the plate. Theprocedure begins by driving a guidewire into each pedicle in step 2010.This is done, of course, after the bone screw locations and trajectoriesare carefully selected, and after a small incision or pair of incisionsare made above the screw locations. Once the guidewires are in place,the plate is advanced to a position over the pedicles in step 2020. Theplate is attached to the remote insertion instrument and advanced byremote manipulation though the incision. As the leading end of plate isadvanced into engagement with each guidewire, each guidewire is snappedthough the split end of the plate and into the plate's channel.

Once the plate is positioned over the guidewires, a first plateorientation assembly is advanced over the first guidewire to properlyorient the plate with respect to the first guidewire in step 2030. Thatis, a first obturator and plate reduction sleeve are assembled togetherand slid down over the first guidewire. The first obturator tip isrotated into alignment with the plate channel and inserted down into thechannel to orient the plate. The first plate reduction sleeve issubsequently secured to the plate to maintain the position of the plate.The first obturator is then removed from the plate reduction sleeve toclear the passage and allow for insertion of a first screw assembly. Afirst screw housing manipulator is loaded with the first screw assemblyand passed over the first guidewire. Once the first screw housingmanipulator is inserted into the first plate reduction sleeve, the firstscrew assembly is driven into the pedicle through the plate in step2040. The first screw assembly is driven downwardly until an indicialine on the first screw housing manipulator aligns with a predeterminedpoint on the plate reduction sleeve. At this point, the first screwassembly is driven to a sufficient depth so that the upper and lowerlocking flanges are in position to engage the plate once the plate isreduced.

The plate is reduced in step 2050 so that the plate extendsperpendicular to the axis of the first screw assembly. In this position,the plate's side rails are axially aligned with and parallel to theupper locking flanges of the first screw assembly, and the plate'slocking grooves are axially aligned with and parallel to the lowerlocking flanges of the first screw assembly. Once aligned, the firstscrew assembly is rotated to lock the assembly to the plate in step2060. The upper locking flange is rotated so that it extends over theside rails, and the lower locking flange is rotated until it enters thelocking grooves in each of the side rails.

In step 2070, a second plate orientation assembly is used to properlyorient the plate with respect to the second guidewire. To accomplishthis, a second obturator and plate reduction sleeve are assembled to oneanother and passed down over the second guidewire. The second obturatortip is rotated into alignment with the plate channel and inserted intothe channel to orient the plate relative to the second guidewire. Thesecond plate reduction sleeve is then locked to the plate to maintainthe position of the plate. Once the second plate reduction sleeve islocked to the plate, the second obturator is removed from the secondplate reduction sleeve to clear the portal in the second plate reductionsleeve. A second screw housing manipulator is loaded with a second screwassembly and passed over the second guidewire into the plate reductionsleeve. Once the second screw housing manipulator is inserted into thesecond plate reduction sleeve, the second screw assembly is driven intothe pedicle through the plate in step 2080. As with the first screwassembly, the second screw assembly is driven down until an indicia markon the second screw housing manipulator aligns with a predeterminedpoint on the second plate reduction sleeve, signaling the point wherethe upper and lower locking flanges are at the appropriate depth toengage the plate. The plate is then reduced in step 2090 to align theplate's side rails 230 and locking grooves 257 parallel with the upperand lower locking flanges on the second screw assembly. The second screwassembly is then rotated to lock the assembly to the plate in step 2100.

In step 2110, the first screw assembly is locked down by tightening thelower locking element so that the lower housing is no longer free toarticulate about the screw head. Compression is then applied to the bonegraft material in the disc space in step 2120. To apply compression, theinserter is operated to advance the second screw assembly toward thefirst screw assembly within the plate channel. After sufficientcompression is applied, the second screw assembly is locked down bytightening the lower locking element in step 2130. At this stage, plateinsertion and adjustment is completed. The inserter, first platereduction sleeve, second plate reduction sleeve, and any otherinstrumentation can be detached from the plate.

The manner in which the individual assemblies and instruments operatewill now be described in greater detail in the following sections, whichdescribe examples of surgical techniques.

Guidewire Insertion/Tissue Dilation

Many of the instruments and assemblies of the present invention aredesigned to be utilized in conjunction with fluoroscopic assistance, asdescribed for example in U.S. Pat. No. 6,945,974, the contents of whichare incorporated by reference. The orientation of each pedicle screw ispre-determined and set by placing a guidewire 350 into each vertebralbody.

To begin insertion of the first guidewire, casing 320 is inserted intoinsertion handle 310, and the first guidewire 350 is advanced throughthe casing. The first guidewire 350 is positioned and oriented over aselected entry point and driven into place using slide hammer 326.Tissue that surrounds casing 320 can be spread open using dilator 400.Dilator 400 is advanced over casing 320 to the bone surface to dilatesurrounding tissue. Once the first guidewire is positioned andsufficient tissue dilation is achieved, the same steps may be repeatedfor subsequent guidewires. All guidewires are placed, and tissue isdilated at each guidewire location, prior to insertion of plate 200.

Plate Insertion

Once the guidewires are properly set, plate 200 may be inserted into theincision and set in the desired position. Inserter 1000 is operable toinsert plate 200 percutaneously through an incision in a minimallyinvasive manner that minimizes the amount of tissue and muscle that mustbe disturbed. Prior to insertion of plate 200, inserter 1000 isconnected with the plate. Distal protrusions 1096 on inserter tip 1094are aligned with and inserted into the shaped aperture 215 on the end ofplate 200. Inner and outer shafts 1009, 1011 are then advanced distallythrough the shaped aperture 215 until tip fitting 1106 reaches threadedbore 216 in the end of the plate. Tip fitting 1106 is threaded intothreaded bore 216 by rotating knob 1060. Once tip fitting 1106 isthreaded into bore 216, plate 200 is secured onto the inserter 1000.Plate 200 is then inserted percutaneously through the incision andmaneuvered through tissue into a desired position. The curvature offlexible shaft 1008 provides a comfortable approach angle that permitsthe plate to be guided into the incision and through the tissue.Positioning of plate 200 can be done with the aid of fluoroscopy orother imaging techniques. Once plate 200 is in the desired position, theplate's position can be fixed by either manually holding the inserter1000 in a stationary position, or by connecting the inserter to a tableclamp or similar apparatus.

Plate Centering and Angling

As noted above, plate 200 must be oriented with respect to the patient'sspine, the guidewires and the screw assembly. The orientation procedurecan be separated into two phases: (1) plate centering and (2) plateangling. In plate centering, plate 200 is positioned so that eachguidewire passes through a centerline of plate channel 250. That is,each guidewire passes through channel 250 at a point that is equidistantfrom the side rails 230. In addition, the axis of the guidewire 350 mustbe parallel to the planes of sidewalls 257.

A first plate orientation assembly 500 is preferably pre-assembled andplaced with the other instrumentation in accordance with standardprocedures for surgical preparation. To assemble the first plateorientation assembly 500, a first obturator 510 is inserted into a firstplate reduction sleeve 550 and turned until indexing detents 514 on theobturator snap into indexing slots 579 in the plate reduction sleeve. Atthis stage, obturator 510 and plate reduction sleeve 550 are lockedtogether axially and radially, enabling the assembled components tofunction as one instrument. Control knob 532 on obturator 510 is turnedto set indicia line 532 a to the unlocked setting. The first guidewire350 is then inserted into the bore in obturator tip 516. Once guidewire350 is inserted into tip 516, plate orientation assembly 500 is advancedover guidewire 350 and lowered into engagement with plate 200. Conicaltapered end 518 of obturator 510 enters channel 250, with the conicalsides engaging side rails 230. Because tapered end 518 is concentricwith guidewire 350, plate 200 is laterally shifted so that the innersidewalls 256 of channel 250 are equidistant from the guidewire 350,thereby centering the plate.

Obturator tip 516 is pressed further downwardly until straight section517 of obturator 510 engages the side rails of plate 200. At this stage,straight section 517 will not enter channel 250 unless flat sides 517 aof the straight section are parallel with side rails 230. The surgeonwill detect a resistance to insertion if the surfaces are not parallel,signaling that the obturator tip 516 is not aligned with the channel250. In such an instance, plate orientation assembly 500 is rotated asnecessary until flat sides 517 a of obturator 510 extend parallel withside rails 230 and align with channel 250. In this orientation,obturator tip 516 passes into channel 250 and captures plate 200 withguidewire 350 centered between side rails 230 and parallel to sidewalls257. As obturator tip 516 enters channel 250, the capturing of plate 200may be sensed by tactile feel. Control knob 532 on obturator 510 isturned to set indicia line 534 to the locked setting. By turning controlknob 532 to the locked setting, inner shaft 522 is rotated until lobes526 push locking springs 536 outwardly. Spring tabs 538 extend throughspring tab slots 520 in obturator tip 516 and pass beneath lowersurfaces 234 of side rails 230. Side rails 230 are thereby capturedbetween spring tabs 538 and the distal end of obturator body 512.Because obturator tip 516 is concentrically positioned around guide wire350, the plate is locked with the guidewire centered in the plate.

Proper engagement between obturator 510 and plate 200 may be confirmedby maneuvering the plate with the obturator. The surgeon checks thatproper engagement with plate 200 is made by carefully moving the plateorientation assembly 500 relative to the plate. Movement should belimited to articulation within the longitudinal plane of plate 200.Proper locking of plate 200 can also be confirmed under lateralfluoroscopy or other imaging techniques.

As obturator tip 516 enters channel 250 to center plate 200 aroundguidewire 350, the plate is also adjusted so that the guidewire isparallel to inner sidewalls 256 of channel 250. Flat sides 517 a ofobturator tip 516 engage inner sidewalls 256 in plate 200 so that thesidewalls are brought parallel to the direction of the guidewire.

The obturator 510 serves to orient the guidewire with respect to theplate 200, as noted above. Obturator 510 also rotationally and axiallyorients the plate reduction sleeve with respect to the plate 200. Oncethe proper orientation of obturator 510 and plate reduction sleeve 550are confirmed, the plate reduction sleeve is ready for axialdisplacement and engagement with the plate.

Plate reduction sleeve 550 is operable in three positions or settingsduring manipulation of plate 200. Once obturator 510 is locked in theproper position, control knob 590 on plate reduction sleeve 550 is movedto a first position to axially unlock the plate reduction sleeve fromthe obturator. In this condition, plate reduction sleeve 550 can beaxially advanced downwardly toward plate 200. The amount of axialadvancement required is preferably indicated by indicia, such as a lineon the exterior of obturator 510. From this position, control knob 590is then moved to a second position to lock the advanced plate reductionsleeve 550 onto plate 200. The locking of plate reduction sleeve 550 toplate 200 can be confirmed by tactile feel, such as by pulling upwardlyon the plate reduction sleeve 550 in a direction away from the plate.Locking can also be confirmed under fluoroscopy. Once plate reductionsleeve 550 is locked to plate 200, obturator 510 can be unlocked fromthe plate and withdrawn out of the plate reduction sleeve, clearing thepassage inside the plate reduction sleeve.

Insertion of First Screw Assembly

Once the plate 200 is properly centered and angled with respect to thefirst guidewire, the first screw assembly is inserted and attached tothe plate. Prior to surgery, appropriate sized bone screws are selectedand preloaded into a first screw housing manipulator 600. The firstplate reduction sleeve 550 provides a portal 551 to introduce the firstscrew housing manipulator 600 to plate 200. To clear portal 551 andprovide access to plate 200, the first obturator 510 is removed from thefirst plate reduction sleeve 550. At this stage, the first obturator isthe only component that is holding the plate 200 in a properly centeredand angled position. Therefore, before obturator 510 can be removed,plate reduction sleeve 550 is secured to plate 200 to preserve andmaintain the centered and angled position of the plate. Plate reductionsleeve 550 is gauged and indexed in a coaxial relationship withobturator 510, so that clamping members 578 are properly oriented toengage side rails 230 of plate 200. Control knob 590 is rotated toretract outer shaft 552 relative to inner shaft 570, thereby openingflex arms 577. This has the effect of releasing plate reduction sleeve550 from indexing detents 514 to disengage the plate reduction sleevefrom obturator 510. Plate reduction sleeve 550 is then slid down overobturator 510 until clamping members 578 pass over plate 200 and detents580 pass beneath lower surfaces 234 of side rails 230. Control knob 590is then rotated to move outer shaft 552 distally over inner shaft andconverge flex arms 577. Clamping members 578 are converged to thepartially engaged condition around side rails 230. Side rails 230 ofplate 200 are captured between inner gripping surfaces 582, but are ableto translate through a small pivot angle. In this condition, platereduction sleeve 550 is clamped over plate 200, but is free toarticulate or “wand” within a plane parallel to the plate. Engagementbetween detents 580 and side rails 230 of plate 200 may be confirmedunder lateral fluoroscopy, or other imaging techniques. With the firstplate reduction sleeve 550 now clamped to plate 200, the first obturator510 can be removed to clear portal 551. Control knob 532 of obturator510 is rotated to the unlocked position to unlock tip 516 from plate200. Once unlocked, obturator 510 is pulled out of plate reductionsleeve 550, clearing portal 551 for introduction of the first screwhousing assembly 100.

The first screw housing assembly 100 is preferably pre-assembled andconnected with a hex driver that engages the head 112 of pedicle screw110. Screw housing assembly 100 and the hex driver are then loaded intothe first screw housing manipulator 600. The loaded screw housingmanipulator 600 is aligned over the proximal end of plate reductionsleeve 550 and portal 551. The distal tip 121 of screw 100 is positionedover the free end of guidewire 350, and the guidewire is slipped intoguidewire bore 124. The screw assembly 100 and screw housing manipulator600 are then passed down over the first guidewire and into portal 551 ofplate reduction sleeve 550. At this stage, it is important to note thatthe orientation of screw assembly 100 is indexed with respect to screwhousing manipulator 600. Screw housing manipulator 600, in turn, isindexed and gauged with plate reduction sleeve 550 so that the axialposition and orientation of screw assembly 100 relative to plate 200 iscontrolled. In the preferred embodiment, portal 551 has diametricallyopposed indexing slots or other alignment features that ensure thatscrew housing manipulator 600 and screw assembly 100 are inserted inproper alignment with plate 200. The alignment features may beconfigured, for example, to only permit screw housing manipulator 600 toenter portal 551 in the proper orientation relative to plate 200.

Once the first screw housing manipulator 600 is inserted into portal551, the first screw assembly 100 is advanced into the plate channel250. Guidewire 350 controls the trajectory of screw assembly 100 as itis passed down through portal 551 and driven into the pedicle.Preferably, the first screw assembly and instrumentation utilizecomponents that minimize the potential for breaking the pedicle surfaceand dislodging or disturbing guidewire 350. In this regard, screw 100preferably includes a self-tapping screw shank configuration that avoidsthe need for assistance with awls or other implements to tap the screw.By avoiding the use of awls, the potential for breaking the pediclesurface and losing the preset guidewire position is minimized. After theshank contacts the pedicle, the driver that is pre-attached to the firstscrew assembly is rotated to begin driving screw shank 120 into thepedicle. The hex driver is turned through a few rotations to begindriving a portion screw shank 120 into the pedicle. After the thread onshank 120 is started and driven a small distance over guidewire 350 intothe pedicle, the angular position of the screw shank is now set. At thispoint, guidewire 350 is preferably removed from the patient as a safetyprecaution to prevent the risk of driving the guidewire through thepedicle. The surgeon then resumes rotating the hex driver to continuedriving the screw 110 into the pedicle. During manipulation of screwassembly 100, it may be desirable to lift plate 200 to an elevatedposition within the tissue to minimize the risk of impingement withspinal processes.

As the hex driver is rotated to drive polyaxial screw 100 into thepedicle, screw housing manipulator 600 advances into plate reductionsleeve 550. The axial position of screw assembly 100 with respect toplate 200 is not visible from outside plate reduction sleeve 550. In apreferred embodiment, the instrumentation includes a set of indicia toindicate when screw assembly 100 is driven to the appropriate depth withrespect to plate 200. Referring to FIG. 30, the first screw housingmanipulator 600 includes an indicia line 649 etched on the exterior ofouter shaft 640. Indicia line 649 is axially positioned to signal whenthe screw assembly 100, and specifically the lower locking flange 134,reaches a depth corresponding to the depth of locking grooves in plate200. An axial distance “X” extends between the locking grooves 257 inplate 200 and the top of control knob 590 when plate reduction sleeve550 engages the plate. The same distance “X” extends between indicialine 649 and lower locking flange 134 of screw assembly 100 when thescrew assembly is clamped by screw housing manipulator 600. In thisarrangement, the top of control knob 590 serves as a guide fordetermining when lower locking flange 134 aligns with locking grooves257 in plate 200. When indicia line 649 aligns with the top of controlknob 590, lower locking flange 134 is located in elevational proximityto locking grooves 257.

It is noted that at this stage, the lower and upper locking elements150, 160 are not locked down in the first screw assembly 100. Lowerlocking element 150 is set in lower housing 130 in an unlocked conditionto allow screw head 112 to pivot against seat 137, so that the screwmaintains a polyaxial range of motion. Upper locking element 160 is alsoset in an unlocked condition to permit sufficient clearance for the siderails 230 of plate 200 between lower locking flange 134 and upperlocking flange 144, as will be discussed.

Plate Reduction

Although screw assembly 100 is advanced into plate 200 with lowerlocking flange 134 in elevational proximity to locking grooves 257, thescrew assembly will most likely be in an incorrect orientation to lockto the plate, as discussed previously. The orientation of screw 110,which aligns with the orientation of the first guidewire 350, is notperpendicular to plate 200 where it intersects the plate. As a result,lower locking flange 134 is not aligned parallel with locking grooves257 and can not rotate into a locked position in the locking grooves. Tobring lower locking flange 134 into alignment with locking grooves 257and plate 200, the screw assembly 100 must be reduced to the orientationof the plate. In particular, lower screw housing 130 must be pivoted androtated about screw head 112 until lower locking flanges 134 is alignedparallel to locking grooves 257. This rotational movement aligns theupper screw housing in a direction perpendicular to the longitudinalaxis of plate 200. Control knob 590 on plate reduction sleeve 550 isrotated to retract clamping members 578 into outer shaft 552. Asclamping members 578 are retracted, plate 200 is displaced relative toplate socket 564, to capture and move the plate reduction sleeve 550 inan orientation perpendicular to the longitudinal axis of plate 200.

Locking the First Screw Assembly to the Plate

Once plate 200 is reduced to an orientation that is perpendicular to thefirst screw assembly 100, lower and upper locking flanges 134, 144 areproperly oriented for locking. To lock the first screw assembly 100 toplate 200, handle 616 of screw housing manipulator 600 is rotatedapproximately 90 degrees to rotate the lower and upper screw housings130, 140. Upper flange 144 rotates until the rows of bosses 145 alignover angled faces 236 of side rails 230. In addition, lower flange 134rotates until the short sides enter into locking grooves 257 in channel250. The arrangement of sharp corners 135 and tapered corners 136 onlower locking flange controls which direction of rotation effectslocking of lower and upper housings 130, 140. The locking grooves 257provide only a small degree of radial clearance for lower locking flange134. The minimal clearance is not large enough to permit sharp corners135 to rotate into the grooves. Tapered corners 136, in contrast, areable to rotate into the locking grooves. Therefore, placement of taperedcorners 136 in the positions shown in FIG. 5, for example, would allowlocking of the housings in response to clockwise rotation of screwassembly 100.

Once lower and upper flanges 134, 144 are rotated into the lockedorientations, side rails 230 of plate 200 are captured in rail slots 146between the lower and upper flanges. Upper locking element 160 is nowtightened over plate 200 to more securely lock the first screw assembly100 to the plate. A driver tool is inserted into passage 611 of screwhousing assembly 600 and inserted into a hex opening in proximal end 162of upper locking element 160. The driver tool is then rotated to tightenupper locking element 160 on screw assembly 100. As upper lockingelement 160 is rotated, the engagement between external thread 164 onthe upper locking element and inner thread 133 in lower housing 130draws the upper locking element into the lower housing. Cap portion 165bears against upper housing 140 and presses the upper housing firmlyonto plate 200. The rows of bosses 145 interdigitate with recesses 238in side rails 230 to enhance the clamping engagement of plate 200 andprovide resistance to longitudinal slippage. Once bosses 145 engagerecesses 238, lower and upper screw housings 130, 140 securely engageplate 200, with side rails 230 captured in rail slots 146. The firstscrew assembly 110 is thereby provisionally locked to plate 200. Inparticular, housing portions 130, 140 of first screw assembly 110 arefixed relative to plate 200. Screw 110 is still free to move polyaxiallyrelative to plate 200, however.

Insertion and Locking of the Second Screw Assembly to the Plate

Once the first screw assembly 100 is locked to plate 200, many of thesteps described above may be repeated for a second screw assembly. Thesecond screw assembly may be manipulated and secured with its owndedicated set of instruments, including a second obturator, a secondplate reduction sleeve and a second screw housing manipulator. Each ofthe dedicated instruments used with the second screw assembly areidentical to the corresponding instruments used with the first screwassembly.

Prior to insertion of the second screw assembly, the plate must bereoriented with respect to the second guidewire location. Reorientationof the plate is done because the first polyaxial screw 110 of the firstscrew assembly 100 has not been locked down, allowing the plate toarticulate relative to the first screw head 112. After plate 200 isoriented with respect to the second guidewire location, the second screwhousing manipulator loaded with the second screw assembly is insertedinto the second plate reduction sleeve and attached to the plate. Thesecond screw assembly is provisionally locked to the plate using thesame procedures used lock the first screw assembly to the plate.

Locking Down the First Screw Assembly

The first screw assembly can be locked down once the second screwassembly is connected with plate 200, and once the desired finalpositioning of the plate is achieved. A driver is inserted into thefirst screw housing manipulator 600, which is preferably left connectedwith the first screw assembly 100. The driver is advanced into the firstscrew assembly 100 until it engages socket 151 of lower locking element150. The lower locking element 150 is then tightened down by torquingthe driver until screw head 112 is tightly locked against seat 137 oflower housing 130.

Because lower housing 130 is free to pivot about screw head 112 duringplate reduction, socket 118 in screw head 112 may not be coaxiallyaligned with the passages through lower and upper locking elements 150,160. The degree of misalignment may be substantial enough to make itdifficult to engage socket 118 using a standard hex driver through thescrew assembly. Therefore, the instrumentation of the present inventionpreferably includes alternative driver implements that permit tighteningof screw heads from angles of approach that are not aligned with theaxis of the screw head sockets. For example, the instrumentation mayinclude a ball-head driver or similar implement that is configured toengage a hex socket and exert torque from an odd angle.

Plate 200 should remain stationary while torque is being applied to lockdown the screw assemblies. To keep plate 200 stationary, acounter-torque is simultaneously applied to plate reduction sleeve 550.To provide a counter-torque while locking down the first screw assembly,a counter-torque assembly is attached to the first plate reductionsleeve 550. The first screw housing manipulator 600 is removed from thefirst plate reduction sleeve 550 and replaced by a first stabilizationsleeve 710. Stabilization sleeve 710 is inserted into portal 551 ofplate reduction sleeve 550 and indexed with inner shaft 570. That is,stabilization sleeve 710 is turned until projections 718 align withindexing slots 584 in inner shaft 570. Sleeve 710 is then advanced intoplate reduction sleeve 550. In the aligned orientation, stabilizingplates 716 are positioned to enter channel 250 and bear against innersidewalls 256. Counter-torque handle 730 is then connected to the firstplate reduction sleeve 550. To attach counter-torque handle 730, pullknob 756 is pulled out of handle body 742 against the bias of spring 752to retract second plug 748 into head 732. Head 732 is then placed aroundcounter-torque coupling 566 on plate reduction sleeve 550. First plug738 is inserted into one of the holes 568 that surround the couplingsurface. At this position, the retracted second plug 748 is aligned withanother of the holes 568. Pull knob 756 is then released, and spring 752projects second plug 748 outwardly into engagement with thecorresponding hole 568 to releasably lock the counter-torque handle 730to plate reduction sleeve 550.

Once counter-torque handle 730 is locked to the first plate reductionsleeve 550, the driver attached to lower locking element 150 can berotated to lock down the lower locking element. As the driver isrotated, an equal and opposite counter-torque is applied withcounter-torque handle 730. The counter-torque is applied to engagementsurface 566 on outer shaft 552, which is distributed to inner shaft 570and stabilization sleeve 710 through their respective alignment members.Stabilization sleeve 710, in turn, distributes the counter-torque fromstabilizing plates 716 to the channel sidewalls 256 in plate 200. Withthis counter-torque, plate 200 is held in a stable position and resiststwisting while torque is applied to lock down the first screw assembly100.

Compression

Plate 200 provides external stabilization to a fusion site. For properfusion to occur, pressure must be maintained on the bone fusionmaterial. Inserter instrument is operable to apply compression to thefusion material. To perform compression, the first screw assembly islocked down using the procedure described above. Once first screwassembly is locked down, the inserter is operated to move the secondscrew assembly in the plate channel 250 toward the first screw assembly.Moving the second screw assembly toward the first screw assembly pressesthe two vertebrae together and applies compression to the bone materialat the fusion site.

To begin compression, inner shaft 1009 of inserter 1000 is advanceddistally into engagement with the second screw assembly 100. Inner shaft1009 is advanced by rotating gear handle assembly 1034. As gear handleassembly 1034 is rotated, pinion 1030 advances rack 1028 distally andpushes inner shaft 1009 distally toward the second screw assembly. Asinner shaft 1009 is advanced, distal tip 1116 advances through the plateend wall and into plate channel 250 until it abuts the second screwassembly 100. The distal end of tip 1116 is axially aligned with notch138 in lower housing 130 of the second screw assembly 100 and advancesinto the notch. The forward progress of the inner shaft 1009 ismaintained by ratchet teeth 1040 on ratchet lever 1038, which preventthe shaft from reversing direction. Ratchet teeth 1040 engage ratchetteeth 1042 on rack 1028 to prevent helical spring 1036 from retractinginner shaft 1009 under the spring bias. As inner shaft 1009 advances,distal tip 1116 pushes the second screw assembly 100 along the platechannel 250 toward the first screw assembly 100. Lower locking flange134 slidably engages the interior of the locking grooves 257 as thescrew assembly 100 is moved. Once second screw assembly 100 reaches adesired position, the upper locking flange can be locked down onto theside rails 230 of plate 200 to fix the position of the screw assemblyrelative to the plate.

After second screw assembly 100 has been displaced to a desired locationalong plate 200, inner shaft 1009 is retracted by depressing finger grip1048 on ratchet lever 1038. Depression of finger grip 1048 pivotsratchet teeth 1040 on lever 1038 out of engagement with ratchet teeth1042 on rack 1028 to release the rack. Helical spring 1036 propels innershaft 1009 proximally back into the inserter 1000, and disengages thedistal tip 1116 from the notch in second screw assembly 100.

Locking Down the Second Screw Assembly

As noted above, the rack and pinion of inserter 1000 includes aratcheted engagement that prevents the inner wire/shaft from reversingor backing out of the plate. In this arrangement, compression force ismaintained against the second screw assembly so long as the instrumentis connected to plate 200. Second screw assembly is then locked down byinserting the appropriate driver into the lower locking element of thesecond screw assembly and tightening the lower locking element in thesame manner described above. Once the second screw assembly is lockeddown, the inserter instrument, first plate reduction sleeve, secondplate reduction sleeve, and any other instrumentation still attached tothe plate can be disconnected from the plate.

While preferred embodiments of the invention have been shown anddescribed herein, both in terms of structure and methods of operation,it will be understood that such embodiments are provided by way ofexample only. Numerous variations, changes and substitutions will occurto those skilled in the art without departing from the scope of theinvention. Accordingly, it is intended that the appended claims coverall such variations as fall within the scope of the invention.

What is claimed:
 1. A method for implanting a spinal stabilizationplate, the method comprising the steps of: inserting an elongated plateinto a space above a first vertebra and a second vertebra, the platehaving proximal end, a distal end and a channel extending between theproximal end and the distal end; advancing a first screw assemblythrough the channel and into the first vertebra; advancing a secondscrew assembly through the channel and into the second vertebra;inserting a pusher member through the proximal end of the plate and intothe channel into contact with the second screw assembly; and advancingthe pusher member in a direction generally parallel to the direction ofthe channel to push the second screw assembly toward the first screwassembly and apply compression between the first vertebra and the secondvertebra.
 2. The method of claim 1 wherein the step of inserting apusher member through the proximal end of the plate comprises advancinga shaft into the channel through a bore that extends through theproximal end of the plate.
 3. The method of claim 1 further comprisingthe step of retracting the pusher member from the proximal end of theplate after compression is applied between the first vertebra and thesecond vertebra.
 4. The method of claim 1 wherein the step of advancinga first screw assembly through the channel and into the first vertebracomprises the steps of advancing a first screw carrier of the firstscrew assembly through the channel and driving a first polyaxial screwcontained in the first screw carrier into the first vertebra.
 5. Themethod of claim 4 further comprising the step of rotating a lockingflange on the first screw carrier into a groove extending along asidewall in the channel to connect the first screw carrier in thechannel in a slidable arrangement.
 6. The method of claim 1 wherein thestep of advancing a first screw assembly through the channel and intothe first vertebra comprises the steps of advancing the first screwassembly over a guidewire driven into the first vertebra.
 7. The methodof claim 6, wherein the step of inserting an elongated plate into aspace above a first vertebra and a second vertebra comprises the step ofpassing the guidewire through an opening in the distal end of the plateand into the channel to position the plate around the guidewire.
 8. Themethod of claim 6, further comprising the step of advancing aninstrument over the guidewire to center the guidewire between the siderails.
 9. The method of claim 6, further comprising the step ofadvancing an instrument over the guidewire to draw the plateperpendicular to the guidewire.
 10. The method of claim 1, wherein thestep of inserting a pusher member through the proximal end of the plateand into the channel into contact with the second screw assemblycomprises advancing an inner shaft through a bore that extendscompletely through the proximal end of the plate so that the inner shaftdirectly contacts the second screw assembly.
 11. A method for implantinga spinal stabilization plate, the method comprising the steps of:inserting a plate into a space above a first vertebra and a secondvertebra, the plate having proximal end, a distal end and a channelextending between the proximal end and the distal end; advancing a firstscrew carrier through a top side of the inserted plate and into thechannel, the first screw carrier containing a first polyaxial screw;advancing a second screw carrier through the top side of the insertedplate and into the channel, the second screw carrier containing a secondpolyaxial screw; inserting a pusher member through the proximal end ofthe plate and into the channel into contact with the second screwcarrier; and advancing the pusher member in a direction generallyparallel to the direction of the channel to push the second screwcarrier toward the first screw carrier and apply compression between thefirst vertebra and the second vertebra.
 12. The method of claim 11wherein the step of inserting a pusher member through the proximal endof the plate comprises advancing a shaft into the channel through a borethat extends through the proximal end of the plate.
 13. The method ofclaim 11 further comprising the step of retracting the pusher memberfrom the proximal end of the plate after compression is applied betweenthe first vertebra and the second vertebra.
 14. The method of claim 11wherein the step of advancing a first screw carrier through a top sideof the inserted plate comprises the step of driving the first polyaxialscrew into the first vertebra.
 15. The method of claim 11 furthercomprising the step of rotating a locking flange on the first screwcarrier into a groove extending along a sidewall in the channel torestrict movement of the first screw carrier to a sliding arrangementalong the length of the channel.
 16. The method of claim 11, wherein thestep of inserting a pusher member through the proximal end of the plateand into the channel into contact with the second screw carriercomprises advancing an inner shaft through a bore that extendscompletely through the proximal end of the plate so that the inner shaftdirectly contacts the second screw carrier.
 17. A method for implantinga spinal stabilization plate, the method comprising the steps of:inserting a plate into a space above a vertebra, the plate having a pairof side rails and a channel between the side rails; attaching a socketelement to the plate after the plate is inserted into the space abovethe vertebra, the socket element containing a polyaxial screw; drivingthe polyaxial screw into the vertebra to attach the plate with thevertebra; actuating a lower locking mechanism on the socket element tosecure the socket element between the side rails in a slidingarrangement along the length of the channel; and actuating an upperlocking mechanism on the socket element to fix the socket element to theside rails and restrict movement of the plate relative to the polyaxialscrew; inserting a pusher member through a proximal end of the plate andinto the channel into contact with the socket element, prior to the stepof actuating the upper locking mechanism; and advancing the pushermember in a direction generally parallel to the direction of the channelto adjust the position of the socket element in the channel.
 18. Themethod of claim 17, wherein the step of actuating a lower lockingmechanism on the socket element comprises rotating a lower lockingflange on the socket element into engagement with a track extendingalong the channel.
 19. The method of claim 18, further comprising thestep of advancing a pusher member through a proximal end of the plateand into the channel into contact with the socket element to push thesocket element along the track in the channel.
 20. The method of claim17, wherein the step of actuating an upper locking mechanism on thesocket element comprises pressing an upper locking flange on the socketelement onto the side rails.
 21. The method of claim 17, wherein thestep of the step of inserting a pusher member through a proximal end ofthe plate and into the channel into contact with the socket elementcomprises advancing an inner shaft through a bore that extendscompletely through the proximal end of the plate so that the inner shaftdirectly contacts the socket element.